This invention relates generally to an apparatus for gripping and holding workpieces, generally defined as workholders, chucks, or sockets in the United States Patent Office classifications, and more particularly is concerned with apparatus which automatically grips and holds the walls forming the aperture in an apertured workpiece.
Up to the present time, milling machines used for milling large workpieces such as, for example, truck or clutch parts, have used conventional rotary indexing mechanisms. One such mechanism commonly used is manufactured by Air Hydraulics, Inc. of Jackson, Mich., and is identified as their Model "H" index table. Indexing tables are usually pneumatic and will include a plate or table to which the workpiece to be milled is clamped. In most cases, clamping members for each workpiece are fabricated and attached to the indexing table. These clamping members generally include wrench-tightenable or lever-actuated members for clamping the workpiece therein. Of course, the operator of the machine must manipulate a wrench to attach and remove the workpiece from the clamping member or insert the workpiece and manipulate the lever. These manipulations are time-consuming and require some judgment as to how tight to turn the nuts onto the bolts and the placement of the workpiece in the clamping member. Any inaccuracy in placement or a failure sufficiently to tighten the workpiece into the clamping members can cause an inaccuracy in the milled workpiece causing the workpiece to be scrapped and resulting in a loss to the manufacturer.
Automatically actuated mandrels have been provided for gripping and holding various types of items including workpieces in certain applications; however, these devices are generally quite complex in structure making them difficult and expensive to manufacture. More importantly, these devices are not capable of being adapted for use on milling machines with automatic indexing tables when the workpieces and the gripping devices must be rotated as a part of the milling operation.